Metcalf is most known to two different generations for two notable roles. In the 1978 college comedy Animal House, he played the sadistic ROTC leader Doug Neidermeyer, who was described in the conclusion of the film (through on-screen captions) as having been "killed in Vietnam by his own troops". He played a very similar character in the Twisted Sister music videos "We're Not Gonna Take It", as the father, and "I Wanna Rock", as a high school teacher. In each video, he used his Animal House catchphrases, "A Twisted Sister pin?!? On your uniform?!?" and "You're all worthless and weak!" respectively.

In the police drama Hill Street Blues, Metcalf had an early key role in the first season as Officer Harris, often clashing with his partner Officer Santini. However, the role was cut short when Metcalf's character was murdered in the episode "Up in Arms".[2]

In the 1997–2003 television show Buffy the Vampire Slayer and its spinoff, Angel, Metcalf played the ancient vampire supervillain, identified in the "BuffyVerse" as "The Master". Coincidentally, he also played a character called "the Maestro", whose real name was Robert "Bob" Cobb, on two episodes of Seinfeld.[3]